1. Field of the Invention
The present invention relates to a solid-state imaging device with simple sensitivity correction and to a signal processing circuit.
2. Description of the Related Art
In a typical CCD (charge-coupled device) solid-state imaging device, stored charges output from two-dimensionally arranged photoelectric converters are sequentially output in an inter-line transfer manner or a progressive scanning manner to output a captured image.
FIG. 4 is a plan view of a typical CCD solid-state imaging device 101.
As shown in FIG. 4, the CCD solid-state imaging device 101 includes a matrix array of photoelectric converters 102, vertical transfer devices 103 between the photoelectric converters 102 in the horizontal direction, and horizontal transfer devices 104 connected to the lower ends of the vertical transfer devices 103. Each of the photoelectric converters 102 photoelectrically converts incident light to generate an electric charge to be stored.
The vertical transfer devices 103 are driven by, for example, a four-phase driving pulse to read the electric charges stored in the photoelectric converters 102 at certain intervals, and sequentially transfer the read electric charges to the horizontal transfer devices 104. The horizontal transfer devices 104 are driven by, for example, a two-phase driving pulse to sequentially transfer the electric charges transferred from the vertical transfer devices 103 to a charge detector 105 via a final horizontal transfer electrode LH. The charge detector 105 stores the charges in a floating diffusion unit FD via an output gate HOG, and outputs an electrical signal via an amplification circuit 106. The charge detector 105 further includes a reset drain RD and a reset gate RG adjacent to the floating diffusion unit FD for discharging the charges stored in the floating diffusion unit FD, if necessary.
Thus, the CCD solid-state imaging device 101 converts electric charges generated by the photoelectric converters 102 into an electrical signal, and outputs the converted electrical signal.
Recent CCD solid-state imaging devices with small chip size and multiple pixels have small cells. However, as the cell size is reduced, the size of photoelectric converters and vertical transfer devices must also be reduced, leading to reduction in dynamic range.
In order to improve the dynamic range, a CCD solid-state imaging device includes a high-sensitivity photoelectric converter and a low-sensitivity photoelectric converter that are adjacent to each other, and an imaging signal output from the CCD solid-state imaging device is processed by an external circuit (see, for example, T. Komobuchi, T. Yamada, A. Fukumoto, Y. Matsuda, M. Masukawa, and S. Terakawa, “Kou Dynamic Range (Wide Dynamic Range) ‘Hyper-D CCD’”, the Journal of the Institute of Image Electronics Engineers of Japan, Vol. 25, No. 4, 1996).
In this approach, the adjacent photoelectric converters 102 of the CCD solid-state imaging device 101 are separated into high-sensitivity photoelectric converters and low-sensitivity photoelectric converters by making the charge storage time of the high-sensitivity photoelectric converters different from that of the low-sensitivity photoelectric converters. In order to form a pixel pair having an adjacent high-sensitivity photoelectric converter and low-sensitivity photoelectric converter, an external circuit adds imaging signals obtained from the high-sensitivity photoelectric converter and the low-sensitivity photoelectric converter. The imaging signal output from the high-sensitivity photoelectric converter is sliced at a certain level before it is added.
In light incident on a CCD solid-state imaging device, the ratio of oblique incident light components in the incident light on pixels in a peripheral portion of the CCD solid-state imaging device is higher than the ratio of oblique incident light components in the incident light on pixels in a central portion of the CCD solid-state imaging device. Generally, oblique incident light components are more diffuse and less focused. Thus, if photoelectric converters in the central portion of the CCD solid-state imaging device are formed in the same fashion as the peripheral photoelectric conversion region, the photoelectric conversion efficiency can be reduced, resulting in low sensitivity.